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The memory manager *may* be implemented in userspace - doesn't have to be.

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Line 1: {{Template:Kernel designs}} == Design == [[Image:Microkernel.png\|frame\|right\|Basic overview of a microkernel]] A Microkernel tries to run most services - like networking, filesystem, etc. - as daemons / servers in user space. All that's left to do for the kernel are basic services, like physical memory allocation (the actual memory '''manager''' may be implemented in userspace), scheduling, and messaging (Inter Process Communication). In theory, this concept makes the kernel more responsive (since much functionality resides in preemptible user-space threads and processes, removing the need for context-switching into the kernel proper), and improves the stability of the kernel by reducing the amount of code running in kernel space. There are also additional benefits for OS's that support multi-CPU computers (much simpler re-entrancy protection and better suitability for asynchronious functionality) and distributed OS's (code can use services without knowing if the service provider is running on the same computer or not). A drawback is the amount of messaging and Context Switching involved, which makes microkernels conceptually slower than amonolithic ~~Monolithic Kernel~~kernels. (This isn't to say that a smartly designed microkernel could not beat a foolishly designed monolithic one.) ~~The~~In ~~"in~~practice ~~theory"~~things ~~starting~~can ~~above~~be ~~paragraph~~quite ~~means~~different. ~~that,~~For ~~yes~~example, ~~your~~if ~~kernel~~the ~~would~~filesystem ~~not~~crashed, ~~crash~~the ~~alongside~~kernel ~~with~~would ~~e.g.~~continue arunning, ~~crashing~~but ~~filesystem. But your~~the user would still belose ~~stuck with~~some data ~~he cannot save,~~- unless ~~you~~provisions ~~made~~were ~~provisions~~made to restart the filesystem server / daemon, and a data recovery system exists. Microkernels can be more stable, but it requires additional design work; ~~and~~it does not come free with the architecture. Likewise, the additional design work that has to be done to get a microkernel design right could also be spent on making a monolithic kernel preemptable. AmigaOS, for example, was a microkernel - and an unusual one: Since the original AmigaOS had no memory protection, its messaging was as quick as it could get (passing a pointer to memory), making the AmigaOS kernel one of the fastest ever devised. On the other hand, that lack of memory protection also meant that the microkernel architecture gave no added stability (later versions did implement MMU support, but at the same speed cost that affects other microkernel systems). Line 13 ⟶ 14: It's also possible for an OS design to borrow concepts from both monolithic kernels and micro-kernels in order to use the benefits of either method where appropriate. == Examples == * Mach * QNX * [[L4]] * AmigaOS * [http://minix3.org Minix] == See Also == === Forum Threads === * [[Topic:10099\|microkernels]] * [[Topic:10234\|discussing microkernel vs modular macrokernel]] ~~==External Links==~~ [http://directory.google.com/Top/Computers/Software/Operating_Systems/Microkernel/ 'microkernel' google directory] ==== Recommended Reading ====▼ [http://www.cbbrowne.com/info/microkernel.html Christopher Browne: microkernel effort] * [http://www.google.com/search?q=The+~~Persistent~~Increasing+~~Relevance~~Irrelevance+of+IPC+Performance+for+Microkernel-Based+Operating+Systems The ~~Persistent~~Increasing ~~Relevance~~Irrelevance of IPC performance in Microkernel-based Operating Systems] by ~~Wilson C. Hsieh, M. Frans Kaashoek, and William~~Brian EN. ~~Weihl~~Bershad▼ ▲====Recommended Reading==== * [http://www.google.com/search?q=The+~~Increasing~~Persistent+~~Irrelevance~~Relevance+of+IPC+Performance+for+Microkernel-Based+Operating+Systems The ~~Increasing~~Persistent ~~Irrelevance~~Relevance of IPC performance in Microkernel-based Operating Systems] by ~~Brian~~Wilson C. Hsieh, M. Frans Kaashoek, and William NE. ~~Bershad~~Weihl * [http://citeseer.ist.psu.edu/408369.html µ-Kernels Must And Can Be Small] by Jochen Liedtke ▲[http://www.google.com/search?q=The+Persistent+Relevance+of+IPC+Performance+for+Microkernel-Based+Operating+Systems The Persistent Relevance of IPC performance in Microkernel-based Operating Systems] by Wilson C. Hsieh, M. Frans Kaashoek, and William E. Weihl [http://~~citeseer~~linuxfinances.~~ist.psu.edu~~info/info/~~408369~~microkernel.html µMicrokernel-~~Kernels Must And Can~~based BeOS ~~Small~~Efforts] by ~~Jochen~~Christopher ~~Liedtke~~Browne * [http://web.archive.org/web/20140803112320/http://i30www.ira.uka.de/~neider/edu/mkc/mkc.html Microkernel Construction Notes] by Raphael Neider [[Category:Kernel]]